Heaters for LTCC-Sensors Made of Resinate Pastes

摘要

Compared to conventional gas sensors, the LTCC technology allows reducing power consumption and structure dimensions. The miniaturization of ceramic microsystems, however, causes new problems to be solved. For example, the heated area of our already presented ceramic hot-plate gas sensor is only about 3.24 mm{sup}2. A further reduction of the structure dimensions requires smaller active elements like heaters. A heater meander of a typical thick-film conductive material should have a large number of squares to achieve a reasonable resistance value. It cannot be easily printed or structured on such a small substrate area. As a solution, metallo-organic (resinate) pastes can be applied. They consist of precious metal compounds (gold, platinum) that are dissolved in organic oils. Besides their low film thickness after firing (about 1μm or less), resinate pastes are much more highly resistive than conventional thick-films. The surface resistance for a gold ink is about 250 mΩ/sq (datasheet value). It allows constructing smaller heaters with a lower number of squares. This paper addresses the application of resinate pastes, particularly for heater applications, on LTCC. Benefits of using resinate pastes as materials for micro-heaters on LTCC are discussed and tested. The electrical properties (resistance, TCR) of gold resinate pastes on LTCC are determined in a temperature range up to 800°C. Possible interaction between metal film and LTCC components were investigated with SEM and EDX. An example for a heater structure made of laser-patterned resinate pastes with a 355 nm Nd:YAG laser is shown.